It is known to use printed circuit boards in which, in a thickness direction therethrough, there are multiple levels of electrical conductors, which have included power layers, ground layers, and layers provided with signal traces, the various layers and traces being in electrical communication with certain contact pins interacting with the PCB and not being in such communication with other such pins, the pins extending all the way through holes in the board of the same diameter throughout board thickness.
It is also known, in PCBs provided with electrically conductive paths only on their two outer surfaces, to provide conductive-surfaced through holes with a larger diameter (in effect counterbores) toward one surface (to accept pins in the counterbores) and with a smaller diameter toward the other surface, to permit increased trace density on that other surface, certain only of the pin-accepting larger holes being through holes at all, the others being blind holes, Igarashi U.S. Pat. No. 4,787,853, "Printed Circuit Board with Through-Hole Connection", granted Nov. 29, 1988.